How To Safely Lower Ammonia Fast in your Aquarium

Ammonia in your aquarium water is something that should be taken very seriously. It only takes a single drop of ammonia in 13 gallons (59 liters) of water to stress and even kill many species of fish.

If your tank is experiencing an ammonia spike, it’s best to act quickly to bring the level down before it can harm your fish.

Here’s how to do it correctly.

How to Lower Ammonia in a Fish Tank Quickly & Safely

Here are some fast-acting solutions you can use to lower ammonia.

Water Conditioner

If you have a water conditioner that detoxifies ammonia, this should be your first step. If your product does not detoxify ammonia, a water change should be your first step. I prefer Seachem Prime as my water conditioner, it’s what I use for water changes, drip acclimating fish and ammonia spikes. 

It binds the toxic ammonia into the nontoxic form ammonium (NH4+). This removes the harm to fish, but still leaves the ammonia in a form that can be eaten by beneficial bacteria eventually, when the biofilter catches up. 

It’s important to note, tests will still show that there is ammonia in the water because aquarium test kits don’t distinguish between bound ammonia and free ammonia. So, the tests will still say there is the same amount of ammonia after you use the water conditioner, but it’s been temporarily bound into a safe form. Follow all product instructions carefully.

Water Changes

Changing out 50% of the water in the tank will immediately cut the amount of ammonia in half. You can repeat water changes every day or every other day until the ammonia spike gets resolved.

Read here for how to perform a water change.


For extreme cases (over 1 ppm), in addition to water changes and conditioner, zeolite can be put in a mesh bag and placed in your filter. It will absorb ammonia from the water column while your filter bed catches up.

Long Term Solutions For Ammonia in Fish Tank

Increased Filtration

The single best solution for long term ammonia control is to increase the amount of biomedia in your filtration system. You can add on simple sponge filters that will greatly increase the surface area for beneficial bacteria to grow on in your tank. They’re a cheap, simple and highly effective way to increase your tank’s filtration. 

Increased water changes

Water changes are both a short term and a long term solution to an ammonia problem. Routinely removing solid wastes from the aquarium means there is less ammonia for the biofilter to have to process. This can be especially important for delicate fish, or really large fish, like Pacu or Arowana. Just eliminate the poop before it can rot. For delicate or large fish, you may need to do large water changes two to three times a week.

Lower stocking levels

Less fish means less waste. Make sure to keep in mind how big your fish will get over time. Larger fish (5 inches/13 centimeters or more) put off tons of waste and can overwhelm your filter’s capacity. I do not recommend overstocking your tank. You can get away with it for a while, but if one little thing goes wrong, it can spell disaster very quickly.

Live Plants

Plants, especially fast growing stem plants and emersed plants, like pothos, can help eat up fish waste byproducts. 

Chemical Filter Media

There are several forms of chemical filtration media that will absorb ammonia, nitrite and nitrate. Just be aware that they can become exhausted, will stop absorbing toxins and will need to be recharged or replaced.

I personally don’t rely on any kind of chemical filtration long term in my tanks; with proper stocking levels, I think it’s expensive and unnecessary, but some folks like to keep heavily stocked tanks that require chemical media. 

  • Seachem Purigen – This would be my first choice. It’s a resin that absorbs nitrogenous wastes, and it can be regenerated.  
  • API Nitra Zorb – another rechargeable filter media that absorbs ammonia, nitrite and nitrate, like Purigen.
  • Fluval Ammonia Remover – This is an ammonia removing resin that needs to be thrown out and replaced each month.
Preview Product
Fluval Ammonia Remover, Chemical Filter Media for Freshwater Aquariums, 3-Pack Fluval Ammonia Remover, Chemical Filter Media for Freshwater Aquariums, 3-Pack
API NITRA-ZORB SIZE 6 Aquarium Canister Filter Filtration Pouch 1-Count Bag, Model:110A API NITRA-ZORB SIZE 6 Aquarium Canister Filter Filtration Pouch 1-Count Bag, Model:110A
Seachem Indoor Purigen Organic Filtration Resin - Fresh and Saltwater 100 ml Seachem Indoor Purigen Organic Filtration Resin - Fresh and Saltwater 100 ml

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Don’t Overfeed

Uneaten food left to rot in your tank puts off a lot of ammonia. Don’t just dump food in and walk away. Carefully watch your fish eat. A little uneaten food is OK. You don’t have to worry about a few stray flakes, but you don’t want large amounts of food sinking to the bottom and decomposing.

Why Ammonia Spikes Happen in Aquariums

Ammonia crops up in aquariums as a result of decomposing fish waste.

Fish create excrete urine and feces, which sink to the bottom of the tank and start to break down. This produces ammonia (NH3). 

Left on its own, more and more fish waste accumulates, producing more and more ammonia, until the tank eventually becomes completely toxic and all the fish will die.

This is why aquarists use filters for their tanks. There is special media inside of aquarium filters called biomedia. Biomedia can be made of a number of different materials: sintered glass, unglazed ceramic, plastic, sponge, etc. Basically, anything porous that water can flow through.

On and inside this media, several species of beneficial bacteria grow that eat ammonia and transform it to a nearly non-toxic form. 

One kind of bacteria consumes the ammonia and turns it into a substance called nitrite (NO2 -1). Nitrite is also highly toxic, but it very quickly gets eaten up and turned into something called nitrate (NO3-).  

At low levels, nitrate is non-toxic to fish, so it can be allowed to build up in the water column in between weekly water changes. 

This process of ammonia being transformed into nitrite and then nitrate is known as the Aquarium Nitrogen Cycle. It is the biggest and most important thing to understand in order to have successful aquariums.

The beneficial bacteria that process ammonia are ubiquitous in almost every environment on Earth. But, it takes time for them to colonize the biomedia in a new tank, in order to build up enough bacteria to handle all of the waste your fish put off.

The most common time for an aquarium to go through an ammonia spike is when it is first set up, because there aren’t any, or not enough, beneficial bacteria to process all of the ammonia.   

Ammonia spikes can also occur if the population of beneficial bacteria in the filter’s biomedia is destroyed, usually from over cleaning or treatment with medications. 

Or sometimes, the tank is overstocked and the filter doesn’t have enough biomedia to keep up with the large amounts of waste produced in the tank.

For more information about the Aquarium Nitrogen Cycle, including how to cycle your tank, please, see our in-depth article here.

Final Thoughts

Ammonia in your tank is bad news, but it can happen, especially in a newly set up tank.

Frequent water changes and treatment with water conditioners can usually get you over the hurdle if you’re performing a fish-in cycle. 

If you have repeated ammonia spikes after your tank has been set up for a while, like say, 4 months or more,  your best bet is to increase the filtration to ensure you have enough biomedia capacity to handle the waste your livestock produces. 

Adding on a simple sponge filter will greatly increase the surface area in your tank for beneficial bacteria to grow on.

Be mindful that overstocking your tank is not a good idea. It leads to an overabundance of waste and can often be very stressful for fish. Trust me, it’s way better to have fewer fish, but a healthier tank!

Ammonia spikes can be stressful, but there are many long term and short term strategies to decrease ammonia and keep it gone.

I hope you find this article helpful.

I wish you and your fish the very best!

Katherine Morgan
Katherine Morgan

Hey, there! I'm Katherine from Northwest Florida. An aquarium specialist, I've kept tanks for over two decades, enjoy experimenting with low-tech planted setups and an avid South American cichlid enthusiast.

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